Odds are your vision includes a home with two kids, as well as two or more cars.

But according to a new study by KPMG, that image is becoming a less common reality. As a growing number of consumers participate in car sharing, wait longer to buy their first vehicle and move to the suburbs, KPMG predicts that in about 25 years, fewer than half of U.S. households will own more than one vehicle.

"We think that the two-car family, over time, it is not going to go down to zero, but a significant amount of people are going to reduce that number," said Gary Silberg, a partner at KPMG who conducted the study.

According to the report, 57 percent of American households currently have two or more cars. Although that percentage has held relatively steady over the last couple of decades, Silberg forecasts it will fall to 43 percent by 2040. That's thanks, in part, to the growing popularity of ride-share companies.

"It is already happening right now. Look at the number of Uber drivers and Lyft drivers," Silberg said. "We think the shared economy is going to be the economy of the future, certainly in automotive."

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Another trend the industry's watching is the fact that many people are waiting to buy their first new car. For decades, automakers have counted on hooking buyers when they're young, and keeping them in the corporate family as they age and buy new models.

But in 2012, automotive research firm Polk estimated the average American would buy four fewer new vehicles in their lifetime, compared with a similar study conducted before the recession. Changing demographics and economics have forced families to reconsider how many automobiles they need.

"The average price of a car is around $31,000. The minute you drive it off the lot you lose 11 percent," Silberg said. "Owning a car is not the most rational economic decision."

Of all the trends pushing families away from owning more than one car, urbanization may be the least appreciated.

But as metropolitan areas grow, so does congestion, and that's forcing families to decide it's easier to use companies such as Uber. As a result, the percentage of American households with at least two cars is much smaller for those living in cities such as New York and Chicago.

"This trend is clear," Silberg said. "More people are moving to cities and suburbs where congestion and costs will make them say they don't need two cars."

Silberg said it's possible that the number of vehicles in the U.S. could start trending lower over the next 20 years, as more families decide not to buy a second car. That could have big implications for automakers' top lines.

But Joe Hinrichs, president of the Americas for Ford, said it's too soon to declare the end of the two-car family.

"It is still a big part of America," he said. "It is suburbia, going to work, going to school. It is going to be a big part of the future, as well."